1. Field of the Invention
This invention relates generally to vehicle suspension systems and, more specifically, to a Progressive Compression Suspension.
2. Description of Related Art
The deserts of southwestern United States have become an adult playground for many people. In these regions, many people spend a great deal of their recreational time and money engaging driving a variety of different types of vehicles around the desert sand dunes. The most widely prevalent vehicle type is the dune or sand buggy. Sand buggies come in a variety of sizes and shapes depending upon their intended use pattern and purpose. There are sand buggies that are essentially cars or trucks with increased suspension travel, large sand-compatible tires, and engines modified to be durable in the hot sandy desert environment.
Other sand buggies go far beyond the basic version described above. These high-end sand buggies have specialized frames, seats, engines, tires and suspension systems so that they can not only be used to drive around the sand dunes, but can actually be raced at high speed in these environments. The suspensions in these high-end sand buggies tend to be an area of particular operational (and therefore design) concern. In sand buggies, having a powerful engine will be worthless if it is being supported by a weak suspension. Particularly because the more powerful the engine, the faster the buggy will go, and therefore the more punishment that the buggy's suspension will sustain. Sand buggy manufacturers and aficionados are constantly in search of new improvements in sand buggy suspensions.
FIG. 1 is a partial cutaway rear view of a conventional sand buggy front suspension 10. As discussed above, there are many shapes and sizes for buggy suspensions, with this version being provided only to give the reader an introduction to the prior art approaches and general layout of buggy suspensions.
The front suspension 10 of a prior sand buggy (half of which is shown here) has a large, ballooning tire 16 attached to a oversized wheel 12. The wheel 12 spins on a short axle 14. A front brake rotor 20 is usually associated with the wheel 12 to provide additional stopping power to the vehicle.
The wheel 12 extends from a spindle 18. The spindle 18 provides the support for the wheel 12 and allows it to be operatively turned by the steering linkage 28 (which is driven by the non-depicted steering system). In its classic form, an off-road front suspension has an upper A arm 22 pivotally connected to the buggy frame 26 and terminating in a swiveling “knuckle” joint at the spindle 18.
Similarly, a lower A arm 24 is also pivotally attached to the frame 26 and also terminates in a knuckle joint at the spindle 18. As should be casually obvious, the pivotal connections at the ends of the upper and lower A arms 22 and 24 will permit the wheel 12 to travel up and down while keeping the tire tread substantially parallel to the ground.
The off road shock assembly 30 is the device that creates the horizontal support necessary to allow the suspension 10 to bear the load of the buggy, as well as permitting the large suspension travel needed for sand activities. The shock assembly 30 of course also provides shock absorption to stabilize the buggy's ride. The shock assembly 30 attaches to the frame 26 at its upper end, and to a midpoint of the lower A arm 24 at its lower end. In this position, the shock assembly 30 will work on the relative motion between the top of the frame 26 and the pivot point where it attaches to the lower A arm 24. The upper A arm 22 simply keeps the spindle 18 upright as the shock assembly 30 permits the lower A arm 22 to travel up and down due to external force from bumps and the like.
The shock assembly 30 used with the prior art off road suspension systems is the focal point of these systems. Most owners of vehicles employing the depicted design will spend substantial time and money improving the performance of the shock assembly 30 in order to improve the overall performance of the suspension 10. The assembly 30 typically has a spring-assisted shock absorber 32, which is a heavy duty shock absorber that has a spring mechanism to provide the suspension with support as well as dampening. Many times, there is also an oil reservoir 34 attached to the assembly 30 to allow for the expanded travel of the shock without enlarging the shock cylinder.
Another approach to improving the shock assembly 30 for off road use is to use a 2-stage spring assembly 36 (versus a single stage). The 2-stages of such a spring assembly provide a spring assisted shock that has different spring tensions for different compression conditions (i.e. lower spring tension when the shock is under low compression, but high spring tension once the low spring tension spring is fully compressed by excessive shock travel). Adding the second spring stage adds cost, of course, and really doesn't improve the mechanics of the suspension 10.
Still another approach for improving performance of the suspension is to add an additional shock absorber that works somewhat in tandem with the two-stage spring shock 30. These “override” shock assemblies are designed to improve suspension dampening when the suspension is at the end of what would be a standard suspension's compressed travel. Adding an override shock also adds substantial cost to the suspension 10, as well as another item that will require periodic replacement.
What is really needed is a new suspension geometry that allows the suspension to use a fairly low-cost single-stage spring-assisted shock absorber, while providing the necessary suspension travel and vibration dampening for high-speed sand travel.